Dyson, of the 16600 block of Winchester Avenue in Markham, allegedly agreed to trade his iPhone for Mastro's PlayStation gaming system after Mastro, of Tinley Park, placed an ad on Craigslist, Assistant State's Attorney Dan Calandriello said.

The two met at the 7-Eleven about 3 p.m. Thursday to make the exchange, Calandriello said.

A video obtained by police shows Dyson putting a box inside a Mercedes Benz, he said.

Mastro retrieved the box, and the two began to struggle over it until Dyson pulled out a gun and shot Mastro in the chest, Calandriello said.

Dyson put the box in his car and sped out of the parking lot, he said.

An eyewitness flagged down an off-duty Tinley Park police officer, who chased Dyson, Calandriello said. Dyson abandoned his car outside an Oak Forest restaurant and ran into a forest preserve, he said. He was arrested after a 45-minute manhunt, police said.